Field of the Invention
The present invention relates to a pipe laying machine and to the related method for laying pipes in a trench.
The invention relates to the field of machinery used to lay medium or large pipes such as oil pipelines, gas pipelines or the like.
Typically, these pipes are assembled directly at the laying site, by welding different tubular sections arranged aligned with one another at the edge of a trench. After being assembled, a stretch of pipe of a given length (tens or hundreds of meters) is buried by placing it on the bottom of a trench, which will then be covered with backfill.
To handle the various sections of pipe, and to lay this pipe in the trench, machines known as pipe laying machines are generally used.
Description of the Related Art
Known pipe laying machines generally comprise a continuous track mounted frame, to which there is applied laterally a boom (or crane) that enables lifting and handling of the pipe. Devices with slings, cradles or the like are wrapped around the pipe to allow it to be gripped and lifted.
Example of these pipe laying machines are described in the patent applications US2003/015488A1, WO2009/045323, US2010/108632A1.
One of the main problems affecting machines of this type is related to the risk of overturning during the laying step when the pipe, which can weigh hundreds of tons, is in the position farthest from the center of gravity of the machine, generating the maximum overturning moment.
For these reasons, to lay a portion of pipe of large dimensions, several pipe laying machines positioned side by side are generally used (up to ten or even more), which lift and lay the pipe in the trench substantially simultaneously. This implies high costs both for the purchase or rental of a large number of machines, and for the use of a higher number of operators to drive them.
To increase the lifting capacity, some of these machines have been provided with appendages or counterweights that move away from the center of gravity of the machine, on the opposite side from the side on which the boom is positioned.
Pipe laying machines thus configured are described, for example, in U.S. Pat. No. 3,938,669A, U.S. Pat. No. 5,332,110A and WO2008/010033 (by the same applicant).
The load bearing capacity of these pipelayers, although greater due to the presence of the counterweights, is nonetheless limited and dependent on the overall dimensions of the machine that, due to problems linked to transport, generally cannot exceed given values.
For these reasons, in order to reduce the number of machines used, and consequently the costs of the work, the machines are often deliberately used beyond their load limits, thus increasing the risk of accidents caused by overturning.
Moreover, pipe laying operations performed with this system have other problems.
In fact, the simultaneous use of several pipe laying machines requires perfect synchronism of the commands imparted by the different operators to the booms during laying of the pipe in the trench. If this synchronism is missing, it is easy to trigger swinging movements of the pipe, which in turn generate dynamic forces capable of overturning the machine even when the static load limit is complied with. Therefore, lifting and laying operations must be performed with particularly slow movements, which affect the times required to complete the work.
Another limit of prior art pipe laying machines and of the related laying method, consists in the fact of having to move very large suspended loads in the vicinity of workers on the ground, who are required to direct and control correct positioning of the pipe in the trench.
Finally, these prior art machines require considerable space on the track at the edge of the trench both in order to pick up the pipe from the ground and for normal travel.